1. Field of the Invention
The present invention relates to a thin-film magnetic head for use for example as a floating type magnetic head in a hard disk device, which is designed to detect, by means of the magnetoresistance effect, a leakage magnetic flux coming from a recording medium, and more particularly to a thin-film magnetic head having a plurality of layers, which can be formed easily, and exhibiting improved performance in terms of detecting a magnetic field, and furthermore to a production method thereof.
2. Description of the Prior Art
FIGS. 12A to 12D are schematic diagrams illustrating a production method of a conventional thin-film magnetic head based on the magneto-resistance effect. FIG. 13 is an enlarged sectional view illustrating a part (the portion denoted by reference symbol XIII in FIG. 12D) of a thin-film magnetic head obtained after completion of the production process.
In a conventional method of producing a thin-film magnetic head, as shown in FIG. 12A, a three-layer film 2 is deposited, by means of for example a sputtering technique, on a non-magnetic material layer (lower gap layer) 1 such as Al.sub.2 O.sub.3 formed on a lower shielding layer. As shown in an enlarged fashion in FIG. 13, the bottom layer of the three-layer film 2 serves as a transverse bias layer 2a for generating a transverse bias field. The transverse bias layer 2a is a soft magnetic layer (SAL) made of a soft magnetic material such as an Fe--Ni--Nb (iron-nickel-niobium) alloy. The layer disposed on the transverse bias layer 2a is a non-magnetic layer (shunt layer) 2b made of for example Ta (tantalum). The top layer is a magnetoresistance effect layer (MR layer) 2c. The magnetoresistance effect layer 2c is made of for example a Ni--Fe alloy.
A resist material is coated on the three-layer film 2 shown in FIG. 12A, and then subjected to an exposing and developing process using a deep-UV technique or the like thereby forming a resist layer 3 having a shape such as that shown in FIG. 12B. As shown in FIG. 12B, the resist layer 3 has undercuts 3a, 3a formed at its lower positions on both sides. The track width (TW) of the thin-film magnetic head is determined by the dimension of the resist layer 3.
The three-layer film 2, except regions on which the resist layer 3 is formed, is then removed using an etching technique such as an ion milling technique, as shown in FIG. 12C. In this etching process, both sides of the three-layer film 2 are removed, and slanted planes (i) are produced. A longitudinal bias layer (hard bias layer) 4 and an electrode layer 5 are then sputtered using the resist layer 3 as a mask so that these layers are formed only in the regions in which the three-layer film 2 is not formed. In the regions near the contacting interface between the three-layer 2 and the longitudinal layer 4 and the electrode layer 5, the thickness of the longitudinal layer 4 and the electrode layer 5 changes in such a manner as shown in FIG. 13 due to the undercuts 3a, 3a formed on the sides of the resist layer 3.
After the resist layer 3 is removed, an upper gap of a non-magnetic material such as Al.sub.2 O.sub.3 is formed on the resultant multi-layer structure shown in FIG. 12, and furthermore an upper shielding layer is formed thereon.
In this thin-film magnetic head, the longitudinal bias layer 4 is a so-called hard bias layer or a hard magnetic layer made of for example Co--Pt (cobalt-platinum) alloy. The magnetoresistance effect layer 2c is magnetized in the X-direction into a single magnetic domain by a magnetic field maintained in the longitudinal bias layer 4. If a detection current is supplied to the magnetoresistance effect layer 2c from the electrode layer 5 via the longitudinal bias layer 4, a magnetic field is induced in the magnetoresistance effect layer 2c by the current, and thus the transverse bias layer 2a experiences a magnetic field in the Y-direction originating from the magnetoresistance effect layer 2c. As a result, the transverse bias layer 2a (the soft magnetic layer) is magnetized in the Y-direction. The transverse bias field in the Y-direction in this transverse bias layer 2a is applied to the magnetoresistance effect layer 2c, and thus the uniform magnetization performed by the longitudinal bias field and the transverse bias field ensure the linearity of the detection output relative to the change in the leakage magnetic field in the Y-direction applied from a recording medium.
FIG. 14 is a front view of a conventional thin-film magnetic head of the spin valve type. The magnetic recording medium such as a hard disk moves in the Z-direction relative to this thin-film magnetic head, while the leakage magnetic field (external magnetic field) from the magnetic recording medium occurs in the Y-direction. The thin-film magnetic head shown in FIG. 14 includes a non-magnetic material layer (lower gap layer) 1 formed of a non-magnetic material such as Al.sub.2 O.sub.3 (aluminum oxide), and a spin valve layer (SV) formed on the non-magnetic material layer, wherein the spin valve layer consists of 6 layers including a lower non-magnetic layer 20 such as a Ta (tantalum), free magnetic layer 21, non-magnetic conductive layer 22, fixed magnetic layer (pinned magnetic layer) 23, antiferromagnetic layer 24, and upper non-magnetic layer 25 such as Ta.
The lower non-magnetic layer 20 ensures that the free magnetic layer 21 formed on the lower non-magnetic layer 20 can have a uniform crystal orientation, and can have a low specific resistance. The free magnetic layer 21 and the fixed magnetic layer 23 are made of a Ni--Fe (nickel-iron) alloy. The antiferromagnetic layer 24 is a bias layer for making the magnetization of the fixed magnetic layer 23 uniformly occur in the Y-direction. That is, anisotropic exchange coupling occurs at the interface between the antiferromagnetic layer 6 and the fixed magnetic layer 23, and as a result the fixed magnetic layer 23 is magnetized in the Y-direction (in the upward direction perpendicular to the drawing plane of FIG. 14) into a single magnetic domain. The antiferromagnetic layer 24 is made of an alloy such as Fe--Mn (iron-manganese), Ni--Mn (nickel-manganese), or Pt--Mn (platinum-manganese).
A longitudinal bias layer 4 such as a Co--Pt (cobalt-platinum) alloy is formed on both sides of the spin valve layer SV having the 6-layer structure described above in such a manner that the longitudinal bias layer is in contact at the contacting interface (V) with all six layers constituting the spin valve layer SV. On the longitudinal bias layer 4, there is further disposed a layer made of a material having a small specific resistance, such as Cu (copper), Ta, or Cr (chromium).
In this thin-film magnetic head of the spin valve type, the longitudinal bias layer 4 is permanently magnetized in the X-direction, and the free magnetic layer 21 is magnetized in the X-direction by a magnetic field from the permanently magnetized longitudinal bias layer 4. The fixed magnetic layer 23 is magnetized in the Y-direction (the upward direction perpendicular to the drawing plane) by the antiferromagnetic layer 24. A steady-state current flows from the electrode layer 5 to the longitudinal bias layer 4 and further into the spin valve layer SV having the six-layer structure in the X-direction. If a magnetic field in the Y-direction is applied from a magnetic recording medium, the magnetization direction of the free magnetic layer 21 is inverted by this external magnetic field from the X-direction to the Y-direction. The electric resistance of the spin valve layer SV changes depending on the relationship between the magnetization direction of the free magnetic layer 21 and the magnetization direction of the fixed magnetic layer 23. Therefore, it is possible to detect the leakage magnetic field from the magnetic recording medium by detecting the voltage drop associated with the steady-state current.
The thin-film magnetic head shown in FIG. 14 can be produced as follows. First, the lower non-magnetic layer 20, free magnetic layer 21, non-magnetic conductive layer 22, fixed magnetic layer 23, antiferromagnetic layer 24, and upper non-magnetic layer 25 are successively sputtered on the non-magnetic material layer 1 thereby forming the spin valve layer SV consisting of these six layers. The spin valve layer SV is coated with a resist material. The resist is exposed to for example deep-UV light, and then developed so that a resist pattern having a width corresponding to the track width (TW) is formed on the spin valve layer SV. Using the resist pattern as a mask. The spin valve layer SV is etched by means of for example an ion milling technique thereby removing the portions of the spin valve layer which are not covered with the resist pattern. In this etching process, the shape of the resist layer formed by the deep-UV exposure and development process affects the shape of the cross section of the resultant spin valve layer SV and thus the width between one contacting face (V) and the other contacting face (V) increases with the contacting position approaching the bottom layer.
The longitudinal bias layer 4 is then formed by performing sputtering using the resist layer remaining on the spin valve layer SV as a mask. Due to the shape of the resist pattern, the thickness of the longitudinal bias layer 4 in the vicinities of the contacting interfaces (V) decreases with the contacting position approaching the top layer as shown in FIG. 14. Except for the vicinities of the contacting interfaces (V), the longitudinal bias layer 4 has a substantially constant thickness. The electrode layer 5 is then formed on the longitudinal bias layer 4.
The thin-film magnetic head having the structure shown in FIG. 13 which is produced according to the process shown in FIGS. 12A to 12D has problems as described below.
(a) In this thin-film magnetic head, the three-layer film 2 and the longitudinal bias layer 4 are in contact at the slanted plane (i) with each other. However, since the magnetoresistance effect layer 2c is located at the top and the longitudinal bias layer 4 is located at the bottom, the longitudinal bias layer 4 in the region (ii) is not parallel to the magnetoresistance effect layer 2c extending in the X-direction. In order for the longitudinal bias layer 4 extending in a slanted direction to magnetize the magnetoresistance effect layer 2c in the X-direction into a single magnetic domain along the plane (i), it is required that the longitudinal bias layer 4 have isotropic magnetic characteristics. To achieve the isotropic characteristics, it is required to form the longitudinal bias layer 4 without introducing magnetic strain. However, this requires difficult sputtering conditions.
(b) The angle and the length L in the X-direction of the slanted plane (i) of the three-layer film 2, and the thickness and the shape of the longitudinal bias layer 4 in the region (ii) are all affected by the shape of the resist layer 3 formed in the process shown in FIG. 12B. The shape of the resist layer 3 is determined by the exposure and the development conditions, and there is a great variation in the shape of the resist layer 3, in particular the shape of the undercuts 3a, 3a. Therefore, it is very difficult to obtain thin-film magnetic heads having small variations from product to product in terms of the angle and the length L of the slanted plane (i) of the three-layer film 2 and the thickness and the shape of the longitudinal bias layer 4 in the region (ii).
(c) Due to the variations in the shape of the resist layer 3, practical thin-film magnetic heads have a small slanting angle of the plane (i) and a great length L in the X-direction. However, if the length L of the slanted plane (i) increases, the transverse bias layer (soft magnetic layer) 2a will have longer portions at its both ends which do not face the magnetoresistance effect layer 2c. The portions of the transverse bias layer 2a extending in the X-direction beyond the ends of the magnetoresistance effect layer 2c are difficult to magnetize in the Y-direction by the magnetoresistance effect layer 2c. As a result, the portions (i) of the transverse bias layer 2a have an independent sensitivity to a leakage magnetic field from a recording medium. This sensitivity affects the detection current, and can be a cause of Barkhausen noise.
(d) When the longitudinal bias layer 4 is formed by performing sputtering using the resist layer 3 as a mask, the material for the longitudinal bias layer has to penetrate into the spaces under the undercuts 3a, 3a of the resist layer 3. Therefore, the deposition rate of the film in these regions is slow, and a great variation occurs in the thickness of the resultant film. In practical production process of thin-film magnetic heads, the longitudinal bias layer 4 is deposited, with the low deposition rate and the thickness variation in these spaces being taken into account. As a result, the portion of the longitudinal bias layer 4 which is not in contact with the three-layer film 2 (or the portion on which resist layer 3 is not present) has an unnecessarily great thickness. This results in a long production time. Furthermore, the total thickness of the magnetic head becomes great. The gap length of the thin-film magnetic film is determined by the thickness of the non-magnetic material layer serving as the lower gap layer and by the thickness of the lower gap layer formed on the three-layer film 2. In recent magnetic heads of this type, it is required to reproduce a signal recorded at a high density and thus a smaller gap length is required. However, if the thickness of the longitudinal bias layer 4 becomes unnecessarily great, the gap length inevitably becomes greater. As a result, it becomes impossible to meet the requirement of the high-density signal reproduction.
On the other hand, the thin-film magnetic head having the structure shown in FIG. 14 has problems described below.
(e) In the conventional structure shown in FIG. 13, since the electrode layer 5 and the longitudinal bias layer 4 are in contact at the slanted plane (i) with the three-layer film 2, the detection current flows from the electrode layer 5 via the longitudinal bias layer 4 not only into the magnetoresistance effect layer 2c but also partly into the transverse bias layer 2a.
(f) In order for the free magnetic layer 21 to be magnetized in the X-direction by the longitudinal bias layer 4, it is required that the longitudinal bias layer 4 can be uniformly magnetized in the X-direction. However, in the regions on the contacting interfaces (V), the thickness (dimension in the X-direction) of the longitudinal bias layer 4 changes in such a manner that the longitudinal bias layer 4 goes up the spin valve layer SV. As a result, it is difficult to uniformly magnetize the longitudinal bias layer 4 in the X-direction. One reason is that in these regions in which the thickness of the longitudinal bias layer 4 changes in the above-described a manner, when an attempt is made to magnetize the longitudinal bias layer 4 in the X-direction, demagnetization occurs randomly in the direction and magnitude. This makes it difficult to magnetize the longitudinal bias layer 4 in the X-direction. Another reason is that since the longitudinal bias layer 4 is in contact with all six layers constituting the spin valve layer SV, the magnetic characteristics of the longitudinal bias layer 4 near the contacting plane (V) change from part to part in response to the changes in the material of the spin valve layer from layer to layer. For these reasons, it becomes difficult to uniformly magnetize the longitudinal bias layer 4 into the X-direction. As a result, the degree of magnetization of the free magnetic layer 21 in the X-direction into a single magnetic domain becomes low, and Barkhausen noise becomes great.
(g) The longitudinal bias layer 4 is in contact with both sides of each of the fixed magnetic layer 23 and the antiferromagnetic layer 24. As a result, the permanently-magnetized longitudinal bias layer 4 exerts great magnetic influences on the fixed magnetic layer 23 and antiferromagnetic layer 24 of the spin valve layer SV. Thus, the fixed magnetic layer 23 is not uniformly magnetized in the Y-direction and great Barkhausen noise occurs.
(h) In order for the free magnetic layer 21 to receive a sufficiently large magnitude of magnetic field from the bias layer 4, it is required that the upper surface 4a of the longitudinal bias layer 4 is located at a position higher than the position of the upper surface of the free magnetic layer 21. To meet this requirement, it is necessary to perform a sputtering process for a long time so that the longitudinal bias layer 4 has a sufficiently large thickness.